The present invention relates to heat transfer element baskets and, more specifically, to improve means for lifting the baskets into and out of an assembly. The present invention has particular application in heat transfer apparatus of the rotary regenerative type.
One type of heat exchange apparatus commonly used for gas-to-gas heat exchange in the process industry and for gas-to-air heat exchange on utility stream generators is the well-known rotary regenerative heat exchanger or air preheater. A rotary regenerative heat exchanger has a cylindrical rotor divided into compartments in which are disposed a mass of heat transfer elements which, as the rotor turns, are alternately exposed to a stream of hot gas and then upon rotation to a stream of cool gas or air to be heated. The heat absorbent mass typically comprises a plurality of heat transfer element basket assemblies which are mounted in sector shaped compartments in the rotor frame. Each of the heat transfer element basket assemblies houses a large number of heat transfer plates which absorb heat from the hot gas and then transfer that heat to the cool gas or air.
As described in U.S. Pat. No. 4,739,822, the heat transfer element basket assemblies may include a stiffening member which is sometimes referred to as a splitter plate. This plate is disposed parallel to the heat transfer plates and located about midway between the inner and outer ends of the basket. As indicated in that prior patent, the stiffening member ties together the structural members of the basket and increases the structural integrity of the frame of the basket assembly. As also indicated in that prior patent, the stiffening member may include lifting holes along the upper region or edge to provide for insertion of lifting hooks. These facilitate the initial placement of the baskets into the rotor frame during field assembly and removal of the baskets for replacement. Also, the baskets adjacent to the cold end of the rotor can undergo severe corrosive duty and these particular baskets are often removed and reversed in position and operated for an additional period of time in that orientation before requiring replacement.
Merely placing holes in a stiffener plate to accommodate a lifting hook has several disadvantages. First of all, the hook can become disengaged from the hole during the lifting operation creating obvious problems. Furthermore, if the stiffening plate extends up above (and below) the heat transfer plates such that the hole is accessible, an undesirable empty or dead space is created within the heat exchanger in the axial space between the stacked baskets which contains no heat exchange surface. This results in an increase in the overall height of the heat exchanger. For that reason, so called low profile baskets are normally used which do not have the extended stiffener plate and corresponding basket framework. In order to have accessible lifting holes, extended tabs are often provided which contain the lifting holes. Once they are lifted into place in the assembly, the tabs are cut off to fit the baskets into the assembly. However, this requires additional time and cost in the field erection process and the lifting holes are no longer available for disassembly.